MOG and erythema multiforme: However, with the further exploration of demyelinating diseases, a lot of studies found that immunopathogenesis of MOG-EM is different from aquaporin-4 antibody positive NMOSDs so that more and more experts classified MOG-EM as a separate disease category.[1] The differences are as follows[2–4]: with the exploration of previous immunological studies, MOG-IgG can directly cause the occurrence of demyelinating diseases; MOG-EM does not damage astrocytes and lacks aquaporin-4 (AQP4) -IgG-positive; MOG-EM and NMOSDs have different histopathological features.